Field of the Invention
The present invention relates to devices for displaying the cooking time of products cooked in automated conveyor ovens such as are typically used in the preparation of pizza, baked goods and the like, and in particular to such a display system incorporating a computing circuit and transducers coupled to provide true cooking time parameters to generate a display of average cooking time when it deviates from prescribed limits.
Automated commercial ovens for the preparation of food are widely used. One class of such ovens are those in which the oven cooking chamber is maintained at a specific cooking temperature or temperatures and food is transported through the oven by means of a conveyor. Typical of such ovens, for example, are those used to prepare pizza. Impingement ovens are also known wherein the food product is heated or cooked by means of streams of hot air impinging thereon as it moves through the oven on the conveyor. Application Ser. No. 386,610, now U.S. Pat. No. 4,438,572, filed June 9, 1982 discloses such an oven, and this application is expressly incorporated herein by reference.
Numerous characteristics of the food such as texture and flavor are directly affected by the length of time required for the food to traverse the oven. Such factors can be even more critical when such ovens are used in such large franchise type operations where the maintenance of uniformity in such characteristics is essential. Accordingly, a variety of such ovens have been developed which provide for control of the operating speed of the conveyor and, correspondingly, the "cooking or baking time". Typically, prior art ovens of this type are provided with a set point controller operatively coupled to the drive motor for the oven's conveyor. In this type of system, some parameter of the conveyor drive motor is controlled, such as, for example, the drive motor armature voltage. However, it has been found that, because prior art control systems monitor an input to the oven rather than the output, substantial variations in bake time can result and can do so without being detected. For example, excessive loading or binding of the conveyor system can cause the conveyor to slow substantially even though a controlled parameter such as armature voltage is maintained constant. Accordingly, while such systems can be periodically checked by means such as a stop watch, such methods are tedious, prone to be neglected, and do not provide an accurate and simple control of this essential parameter to the desired accuracy.
The input speed of the prime drive element can be monitored continuously, however, in addition to the above-discussed problems, it is not uncommon for input speed variations to fluctuate at a relatively high rate. A common result is that an operator, noticing a particular fluctuation, will change the conveyor speed to correct and this adjustment may itself be too large or the variation in speed may be a temporary occurrence whereby the alteration of the oven's bake time set point will itself produce an error. This is particularly true when the oven operator is a relatively unskilled person, which frequently occurs in large franchised restaurant chains.
Accordingly, there exists a need for an improved bake time control and display system for use with a food preparation oven which will obviate these difficulties.